﻿1861.] 



MURCHTSON AND GELKIE — HIGHLANDS. 



213 



occur abundantly, too, on the opposite island of Easdale, where they 

 present some interesting features in relation to the different rates at 

 which the various parts of the dykes cooled. 



The slates of Easdale and Seil present perhaps the most perfect 

 cleavage yet known in Scotland. The cleavage-planes lie in the 

 same direction as the bedding — that is, towards the south-east — but 

 generally at a higher angle. The following list of observations, taken 

 from Easdale, across the strike of the Seil slates, will show the ratio 

 of the two planes : — 



Easdale (south side): slates dip S. 62° E. at 32° ; cleavage same direction at 50°. 



„ „ S. 46° E. at 25° ; „ „ 45°. 



„ „ S. 64° E. at 68° ; „ „ 42°. 



Seil Harbour „ S. 54° E. at 82° ; „ „ 55°. 



„ (west shore) „ S. 43° E. at 27° ; „ „ 55°. 



S. 40° E. at 33° ; „ „ 57°. 



S. 52° E. at 27° ; „ S. 42° E. 42°. 



„ (1 mile N.W. of Kirk) S. 60° E. at 60°-67° ; „ 60°-70°. 

 ., (old slate-quarries) ,, obscure dip ; ,, S. 66° E. 27°-45°. 



„ (100 yds. N. of last obs.) S. 60° E. 60°-70° ; „ S. 66° E. 40°. 

 „ (eastern shore) „ S. 68° E. 25° ; „ S. 66° E. 62°. 



The bedding of the slates is distinctly denned both by lines of 

 colour and by the intercalation of seams of hard blue sandy mud- 

 stone, nodules of which also occur in the slate. The cleavage is most 

 perfect where the slate is finest in grain ; some of the sandy beds are 

 only rudely cleaved, and others show no cleavage at all. The sur- 

 faces of the cleavage-planes are finely waved or foliated, and contain 

 numerous cubes of iron-pyrites. 



Eastern Shores of Linnhe Loch. — The slates of Seil and Easdale 

 are soon lost in their northward prolongation under the sheets of 

 greenstone and underlying reddish sandstones * that form so large a 

 tract in Lorn. North of Oban, however, we find the quartz -rock or 

 quartzose flagstones rising in terraces along the east coast of Loch 

 Linnhe, especially in the neighbourhood of Port Appin. They are 

 covered by the upper limestones and schists as in Islay, and are 

 clearly underlain by the thick limestone of Lismore. The section 

 at this place therefore forms the counterpart of that of Islay to tho 

 south, and that of Ross and Sutherland to the north. 



Glen Spean. — The same order of succession continues up the Great 

 Glen, which, as we have already shown, coincides with the line of an 

 anticlinal axis. The quartzose strata which have been described as 

 occurring at the head of Loch Eil, and thence eastwards to Banavie, 

 roll over to the south-east, and are followed by schistose beds con- 

 taining several seams of limestone. The stream in Glen Spean, on 

 the north side of Ben Nevis, shows the succession well. At the 

 Bridge of Spean, quartzose and schistose strata dip S. 55° E. at a 

 high angle. Quarter of a mile to the eastward, quartzose flagstones, 

 much altered, with intercalations of bluish-grey micaceous and talcose 

 schist, dip S. 62° E. at 65° to §b°. This same quartzose series con- 



* The thick-bedded, very hard, greenish, siliceous sandstone on Loch Eeoehan, 

 south of Oban, is undistinguishable from many portions of the Old Red Sand- 

 stone, but may be of later age. 



VOL. XVII. — PART I. Q 



